Thelma is the middle child and only daughter of Florida and James Evans Sr. She grew up on the Southwest-side of Chicago in a cold water flat housing hi-rise project building with her parents and older brother, J.J.. When her mother was pregnant with her younger brother Michael, the family moved to the North-side of Chicago in The Housing Projects. As Thelma became a teenager, she became interested in acting, dancing and in dating men. Her favorite actor was Billy Dee Williams and her favorite musicians were Isaac Hayes, Stevie Wonder, and Marvin Gaye. Thelma had various boyfriends and fiancées.

Thelma is not afraid to stand up to her older brother J.J. and any other person who tries to take advantage of her. She's a "daddy's girl," and her father can be over-protective from time to time. But that doesn't stop Thelma from being obsessed with boys (and accepting a few marriage proposals!). Like the rest of her family, she also dreams of moving out of her housing project. But until the day that dream is realized, Thelma does her best to be as much help as she can to her mother and around the house. Her constant fighting with J.J. is too much for her parents to deal with at times, but their love for each other is deep. With her family behind her, Thelma is reassured that she will survive her teenage suffering.

Thelma met, courted, then married former standout collegiate football star Keith Anderson in 1978 at the beginning of Season 5, a college athlete who had a bright future, in being the top draft choice of the NFL's Chicago Bears. But at their wedding, Keith tripped over J.J. who was taking wedding day pictures, breaking his leg. This event led to Keith developing a drinking problem and eventually getting a job as a taxicab driver. By series' end, in the final episode, Thelma and Keith were moving into a new apartment near Lake Michigan after Keith completely recovered from his knee and leg injuries had finally got his multi-year contract to play football for the Chicago Bears. She then invited soon-to-be grandma, Florida to live along with her because of her pregnancy since she would need help taking care of the baby. At the end of the series Thelma and Keith were expecting.